1. Field of the Invention
The invention relates to technical fields in which colors must be recognized, particularly relating to color recognition in electronic reproduction technology.
2. Description of the Prior Art
Method for recognizing colors are known from the German Patents (patent application Nos. P 29 23 473.9, P 29 23 468.2 or P 29 23 477.3) in which, before the actual color recognition, the color components of at least one characteristic sample point are opto-electrically determined in each color to be discriminated, whereby the color components represent the spatial coordinates of the respective color locations in the three-dimensional color space. Color numbers are allocated to the color component triads of the measured sample points and the color numbers are deposited under those addresses of a color recognition memory which coincide with the appertaining color component triads. In the color recognition memory, each memory location corresponds to a color location of the color space.
Subsequently, the still-missing color numbers of the remaining color locations are automatically determined from the color numbers of the sample color locations and are likewise deposited under the corresponding addresses of the color recognition memory. All color locations occupied with the same color number respectively form a bounded color recognition space of one color or of a spatial color region within the color space.
During the actual color recognition, the colored surfaces to be analyzed are opto-electrically scanned point and linewise and the color components thereby gained call in the corresponding addresses of the color recognition memory. The color numbers deposited there are read out, whereby the association of the scanned colors to the bounded color recognition spaces is determined.
The size, shape and position of a color recognition space in the color space determine the spatial color region which is evaluated in the color recognition as belonging to one color. For the purpose of a precise color determination, therefore, it is necessary that the boundaries of the individual color recognition spaces be matched as well as possible to the color regions to be separated. In the known method, this demand is met by a sufficiently large plurality of targeted color samples taken per color region. Nonetheless, in practice, it occasionally turns out only after the color recognition, for example, on the basis of a color separation, that, for the purpose of an even better color separation, the limitation of one or more color recognition spaces must be partially changed or that the color space must be subdivided into even finer color recognition spaces. In this case, given the known method, new color samples must be taken, the color numbers must be recalculated, and the color recognition memory must again be filled. These measures, however, mean a longer preparation time for the actual color recognition.
Refer to FIG. 6 which shows the Prior Art.
The image to be analyzed may be an image or pattern for multiple color printing, or for textile printing, decorative printing or package printing, or also a design pattern for obtaining control data for textile processing machines. The colored image may include a color printing medium and generally any colored surface or plane.
The colored image will generally include separate, adjoining colors, and colors vignetting into one another. The individual colors may, for example, due to color tolerances or due to an irregular application of the color, show color deviations. During color recognition, the problem arises to separate the individual colors from one another, or, if necessary, to combine color deviations in the colored image into a single color. In colors vignetting into one another, namely in colors showing gradual saturation and/or brightness changes, such color deviations have been intended by the designer. The color recognition process must cope with the problem to either separate the colors vignetting into one another, or, if necessary, to combine some colors vignetting into one another into a single color.
The colored image 1, which is mounted on a carrier 2, is illuminated by two light sources 3 and 4 of known spectral composition, and the reflected or transmitted scanned light passes via lenses 5 and 6, and via a light stop 7 to a scanner 8. In the scanner 8, the scanned light is split by means of two dichroitic color separators 9 and 10 into three partial beams, which pass through color correction filters 11, 12 and 13 and impinge on three photoelectric transducers 14, 15 and 16 respectively. The transducers 14, 15 and 16 transform each partial light beam according to the intensities of the color components of the scanned colors into trichromatic color-measuring signals red, green and blue, which represent the spatial coordinates of the associated color locations in the cartesian red, green and blue color space.
Each trichromatic color-measuring signal red, green and blue passes through a logarithmic stage 17, where it is amplitude or gamma-corrected and/or modified according to a predetermined gradation curve.
In a color converter stage 18, the trichromatic color-measuring signals red, green and blue are transformed by an appropriate matrix into chrominance signals x and y, and into a luminance signal z according to the relations: EQU x=a.sub.11 R+a.sub.12 G+a.sub.13 B EQU y=a.sub.21 R+a.sub.22 G+a.sub.23 B EQU z=a.sub.31 R+a.sub.32 G+a.sub.33 B
This matrix transformation corresponds to a transformation of the red, green and blue color space into a chrominance-luminance color space. The chrominance signals x and y represent the color coordinated of the color locations in the chrominance plane, and the luminance signal z represents the third coordinate or grey axis. Transformations of this type are known in color television.
The chrominance signals x and y, and the luminance signal z are converted in analog-to-digital transducers 19, 20 and 21 into digital signals, each signal having a word length of five bits each, which signals pass to outputs 22, 23 and 24 respectively. Digitizing of these signals may be accomplished with different respective quantizations.
The outputs 22, 23 and 24 of the analog-to-digital transducers 19, 20 and 21 are fed to an address bus 32, which is connected to an address input 29 of a color recognition memory 28 through a switch 33. Said color recognition memory 28 has a plurality of storage locations representing the individual color locations of the color space. Each storage location is addressable by these digital signals x, y and z, which represent the color coordinates of the respective color location. Identification symbols for the colors to be recognized in the form of color numbers are stored in the individual storage locations of the color recognition memory 28.
During the actual color recognition process, the scanner 8 then scans the colored image 1 point by point, and line by line, by a relative movement between the scanner 8 and the image carrier 2. The color coordinates, or equivalent addresses obtained thereby, then call up, via the address bus 32 and the switch 33, the corresponding color numbers in the color recognition memory 28, which are then read out via the data output 31 from the color recognition memory 28, whereby the colors are identified. The switch 33 is then positioned in the position shown dotted.
Preparatory to color recognition the individual color recognition spaces for the colors to be identified must be separated within the color space by assigning respective color numbers to the color locations of the color space or respectively to the storage locations of the color recognition memory 28. The filling process is accomplished by the following method steps:
(a) selecting in said colors of said image a number of sample points, each sample point having a sample point color and measuring the color coordinates of the sample color locations of said selected sample point colors; PA1 (b) defining an identification symbol or color number for each selected sample point color to be recognized and assigning the defined color numbers to the sample color locations around which color recognition spaces are to be built; and PA1 (c) building up the individual color recognition spaces by filling the color recognition memory with respective color numbers in the steps of: surrounding the sample color locations with selected color locations so as to form shells of successively increasing size around the sample color locations, calling-up said selected color locations shell by shell at successively increasing distances from the sample color locations, checking each called-up color location to determine whether a color number has already been alloted thereto, and assigning the color number alloted to a corresponding sample color location to said called-up color location if no color number has already been alloted to said called-up color location. After said color recognition memory 28 has been filled up in the described way all color locations bearing the same color number forming a color recognition space for the selected sample point color defined by said color number.
That method steps are carried out with the aid of the scanning member 8 and a color processor 34'.
The color processor 34' includes an input stage 35, a sample point memory 36, an address control stage 37, a calculating or processing stage 38' and a shell memory 62. The input stage 35 includes a first operator area 35', on which there are disposed ten keys for the selection of the color number, and a second operator area 35", which includes a plurality of operating keys.
The operation of the color processor 34' will now be explained further below.